Definition
Checking the specific gravity of urine is a quick, non-invasive test that evaluates how well the kidneys concentrate or dilute urine. It reflects the density of urine compared to water and helps assess hydration status, renal function, and certain metabolic conditions.
Purposes
- To determine the level of concentration of urine.
- To diagnose conditions, such as diabetes insipidus, SIADH.
- To assess kidney function.
- To monitor Hydration status
- To guide fluid therapy.
Articles
- Container to collect urine.
- Calibrated urinometer.
- Jar for urine.
- Clean gloves.
Methods of Measurement
| Method | Description |
|---|---|
| Dipstick Test | A chemical strip changes color based on ionic concentration; quick but less precise |
| Refractometer | Measures light refraction through urine; more accurate and commonly used in labs |
| Urinometer | A float-based device that measures density; requires a large urine volume and temperature correction |
Normal Range
- 1.005 to 1.030 is considered normal for random samples
- Values <1.005 suggest dilute urine (e.g., overhydration, diabetes insipidus)
- Values >1.030 suggest concentrated urine (e.g., dehydration, SIADH, glycosuria)
Clinical Significance
| High Specific Gravity | Low Specific Gravity |
|---|---|
| Dehydration | Overhydration |
| Glycosuria (e.g., diabetes mellitus) | Diabetes insipidus |
| Proteinuria | Renal tubular damage |
| SIADH | Chronic kidney disease |
Pre-Analytical Considerations
- Use first morning urine for best accuracy
- Avoid testing after contrast dye procedures
- Refrigerated samples must be brought to room temperature before testing
- Glucose or protein in urine can falsely elevate readings with refractometers
Procedure
| NURSING ACTIONS | RATIONALE | |
| 1. | Before procedure Explain procedure to the patient and provide container to collect urine. | Facilitates cooperation of the patient to collect urine. |
| 2. | During procedure Don gloves. | Reduces risk of contamination. |
| 3. | Fill three fourths of jar with urine. | Permits urinometer to float free in urine. |
| 4. | Gently place urinometer into jar. | |
| 5. | Make sure that instrument floats freely and does not touch bottom and sides of jar. | If urinometer touches the jar, reading will be false. |
| 6. | When urinometer stops bobbing, read specific gravity directly from scale marked on calibrated stem of urinometer. Read scale at lowest point of meniscus to ensure an accurate reading at eye level (normal specific gravity of urine is 1.010-1.025). | Reduces errors of reading. |
| 7. | After procedure Discard urine, and rinse jar and urinometer in running water. | Prevents contamination. |
| 8. | Remove gloves and wash hands. | Reduces transmission of microorganisms. |
| 9. | Replace articles and record the procedure in nurse’s record or flow sheet according to policy. | Recording gives information about the procedure results to health workers. |
Special Consideration
When collecting a urine sample for specific gravity testing, precision and preparation are key to ensuring accurate results. Here are the most important special considerations to keep in mind:
Special Considerations for Collecting Urine for Specific Gravity
| Consideration | Rationale |
|---|---|
| Use first morning urine | It’s the most concentrated sample, ideal for assessing kidney concentrating ability. |
| Avoid recent contrast dye exposure | Radiographic dyes (e.g., from CT/MRI) can falsely elevate SG readings. |
| Maintain sample temperature | Refrigerated samples must be brought to room temperature before testing to avoid skewed results. |
| Avoid contamination | Use the clean-catch midstream method to prevent bacteria or debris from affecting results. |
| Note medications and diet | Diuretics, glucose, protein, or certain foods (e.g., beets, rhubarb) can alter SG. |
| Avoid testing during menstruation | Menstrual blood can falsely elevate SG—delay testing if possible. |
| Label and time the sample | Accurate labeling ensures proper interpretation and avoids mix-ups. |
REFERENCES
- Annamma Jacob, Rekha, Jhadav Sonali Tarachand: Clinical Nursing Procedures: The Art of Nursing Practice, 5th Edition, March 2023, Jaypee Publishers, ISBN-13: 978-9356961845 ISBN-10: 9356961840
- Omayalachi CON, Manual of Nursing Procedures and Practice, Vol 1, 3 Edition 2023, Published by Wolters Kluwer’s, ISBN: 978-9393553294
- Sandra Nettina, Lippincott Manual of Nursing Practice, 11th Edition, January 2019, Published by Wolters Kluwer’s, ISBN-13:978-9388313285
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